Flexible expandable vascular support

ABSTRACT

The invention relates to an expandable insert for use as a vessel support in blood vessels, the insert being able to deform plastically from a nonexpanded state to an expanded state by application of a radial force directed from the inside outward, with at least one tubular, essentially cylindrical main body section, whose circumferential surface is formed by a number of annularly meandering rings, the rings in each case forming a one-piece strand of material with a defined strand length. The insert is particularly stiff with respect to externally acting radial forces because a first group of rings is provided whose strand length essentially corresponds to the circumference of the insert in the expanded state, and a second group of rings is provided whose strand length is greater than the circumference of the insert in the expanded state.

The invention relates to an expandable insert having the features of thepreamble of claim 1.

Such inserts, also called stents, are known from U.S. Pat. No. 5,102,417and from U.S. Pat. No. 5,195,984.

The known inserts have three tubular sections or segments which are madeof an implantable material. The three tubular segments are eachconnected to one another via bridge members which are intended to allowthe segments to tilt or cross in relation to each other.

The individual segments are formed by cutting out rectangular blanksfrom the jacket of the tubular segments. Blanks adjacent to each otherin the circumferential direction are offset in relation to one another.The rectangular blanks have axially parallel long sides and narrow sidesrunning in the circumferential direction. The narrow sides at the endsare not interconnected, so that due to free spaces the end face of thetubular segment has a crenelated appearance. In the known inserts, theinterconnected segments are oriented coaxial to one another in the statewhen the insert is not in use, and they are connected by bridges betweenthe narrow sides at the ends. In U.S. Pat. No. 5,102,417, straight,parallel bridge members run obliquely from one end face of a segment inthe direction toward the narrow side adjacent to the opposite narrowside in the circumferential direction. Each narrow side of a segment isconnected to a narrow side of the adjacent section, so that theobliquely extending bridge members give the insert a twisted appearance.

U.S. Pat. No. 5,195,984 discloses an insert in which adjacent segmentsare in each case connected via a straight, axially parallel bridgebetween two exactly opposite narrow sides. Between each segment there isonly one bridge member, so that the space between the segments remainsessentially free.

In practice, these inserts, with small material thicknesses, are notsufficiently stiff with respect to compression in the radial direction.

The object of the invention is therefore to provide an expandable insertfor use as a vessel support in blood vessels, in which, together withsufficient flexibility for adaptation to the curvatures of the vessels,there is a particularly high level of resistance (recoil) to forcesexerted radially from the outside.

This object is achieved by means of an expandable insert having thefeatures of claim 1.

Because a first group of rings is provided whose strand lengthessentially corresponds to the circumference of the insert in theexpanded state and a second group of rings is provided whose strandlength is greater than the circumference of the insert in the expandedstate, the rings of shorter strand length can efficiently take upcompression forces, while the rings of greater strand length coverrelatively uniformly the interspaces which arise between the rings ofthe first group. The rings of the second group additionally permit aflexibility of the insert under bending stresses within the necessaryrange.

It is advantageous if the strand length of the second group is 1.2 to2.0 times as great as the strand length of the first group, inparticular 1.3 to 1.5 times as great, because under these conditions agood relationship is obtained between expandability and shortening oflength during expansion. Increased flexibility in relation to bendingstresses is obtained if the strand length of the second group is 1.7 to1.9 times as great as the strand length of the first group.

An arrangement with good coverage of the interspaces which arise isobtained if the meandering strands of the second group have lengthsections which in the nonexpanded state run parallel to the center axisof the main body. In addition, with regard to stability, it isadvantageous if the meandering strands of the first group havecircumferential sections which in the nonexpanded state run in thecircumferential direction of the main body.

A particularly advantageous construction is obtained if the strands ofthe first group and the strands of the second group each intersect inthe area of the length sections, in particular if the circumferentialsections of the first group are connected centrally to the lengthsections of the second group.

A very uniform pattern of opening of the insert in the expanded state isobtained if the number of the periodically recurring meanderings of astrand of the first group is twice as great as the number of meanderingsof a strand of the second group, for example if the meanderings of thefirst group have three or four periodic segments and the meanderings ofthe second group correspondingly have six or eight periodic segments.

An illustrative embodiment of the invention is set out below withreference to the drawing, in which:

FIG. 1 shows the unwound circumferential surface of an expandable vesselsupport in the nonexpanded state; and

FIG. 2 shows the circumferential surface of an expandable vessel supportaccording to FIG. 1 in the expanded state.

FIG. 1 shows the unwound circumferential surface of a cylindrical,tubular vessel support in the nonexpanded state.

The circumference section 1 is shown in a plan view, with the main body,which is cylindrical and tubular per se, being shown sectioned along anaxis-parallel cutting plane 2 and spread out flat. The circumferentialsurface is made up of a number of meandering material strands 3 a, b and4 a, b. The material strands 3 a and 3 b are looped in a meandering orundulating configuration in the circumferential direction of the insert,almost semicircular curve sections 5 alternating with straight,axis-parallel length sections 6. In the illustrative embodimentaccording to FIG. 1, the strand length of the encircling material strand3 a or 3 b is approximately 14.5 mm, which, in the configuration shown,gives a diameter of 1.8 mm in the nonexpanded state. The meanderingstrand 3 a or 3 b can be considered as a periodically recurring form,each period comprising two length sections 6 and two curve sections 5.In this illustrative embodiment, therefore, there are three periodicareas arranged in the circumferential direction.

The material strands 4 a and 4 b are likewise arranged in a meanderingconfiguration around the circumferential direction. Here too, curvesections 7 alternate with length sections 8, the length sections 8 inthe nonexpanded state of the insert running approximately parallel tothe length sections 6 of the material strands 3 a and 3 b. The materialstrands 4 a and 4 b also have a periodicity, the number of periods inthis illustrative embodiment being twice as great as the number ofperiods of the material strands 3 a, 3 b. In FIG. 1, the illustrativeembodiment has six periodic sections. In the present illustrativeembodiment, the length of the material strands 4 a, 4 b is approximately11 mm, which again, in the present configuration, leads to a diameter of1.8 mm.

In the present illustrative embodiment, the material strands 3 a and 3 bpass through each other approximately centrally in the respective lengthsection 6 of the material strand 3 a, 3 b. The material strands 4 a, 4 bhere pass through the material strands 3 a, 3 b approximately at rightangles.

In practice, the expandable insert according to the invention is cut asa single-piece element from a tube having the external diameter of 1.8mm. A suitable material which can be used here is in particularimplantable stainless steel, but other implantable materials can also beused. The material thickness in the radial direction is essentiallyconstant over the entire area of the insert.

In FIG. 2, an insert according to FIG. 1 is shown in the second,expanded state. The diameter of the insert in the expanded state is 3.5mm in this illustrative embodiment. The resulting deformation throughusing a force acting radially from the inside leads to the materialstrands 4 a and 4 b being fully stretched, i.e. forming in practice acircular ring of 11 mm circumference. In the present configuration, thelonger material strands 3 a and 3 b are deformed into undulating, almostsinusoidal material strands.

The material strands 4 a and 4 b of circular ring shape in the expandedstate provide a strong structural resistance to a radial force actinguniformly from the outside, which resistance reliably prevents collapseof the insert in the treated blood vessel. Alternatively, with the sameresistance force (recoil), a smaller material thickness can be usedcompared to the known inserts. In both cases, the danger of renewedcross-sectional narrowing of the treated blood vessel, also calledrestenosis, is less than with the known inserts.

The use of the insert in practice is known in principle.

When employed, the inserts according to the invention are introducedwith a balloon catheter into the blood vessels that are to be treated.The balloon catheter is widened by injecting a fluid, whereupon theinserts expand permanently in the radial direction by means of plasticdeformation.

After the balloon catheter has been removed, the insert remains in theblood vessel and is in a short time enclosed by the tunica intima.

Of course, other configurations also afford the advantages according tothe invention. Thus, for example, Ω-shaped configurations areconceivable.

What is claimed is:
 1. An expandable insert for use as a vessel supportin blood vessels, the insert being able to deform plastically from anonexpanded state to an expanded state by application of a radial forcedirected from the inside outward, with at least one essentiallycylindrical main body section, whose circumferential surface is formedby a number of annularly meandering rings, the rings in each caseforming a one-piece strand of material with a defined strand length,wherein a first group of rings is provided whose strand lengthessentially corresponds to the circumference of the insert in theexpanded state, and a second group of rings is provided whose strandlength is greater than the circumference of the insert in the expandedstate.
 2. The insert as claimed in claim 1, wherein the strand length ofthe second group is 1.2 to 2.0 times as great as the strand length ofthe first group.
 3. The insert of claim 2, wherein the strand length ofthe second group is 1.3 to 1.5 times as great as the strand length ofthe first group.
 4. The insert of claim 2, wherein the strand length ofthe second group is 1.7 to 1.9 times as great as the strand length ofthe first group.
 5. The insert of claim 1, wherein the meanderingstrands of the second group have length sections which in thenonexpanded state run parallel to the center axis of the main body. 6.The insert of claim 1, wherein the meandering strands of the first grouphave circumferential sections which in the nonexpanded state run in thecircumferential direction of the main body.
 7. The insert of claim 1,wherein the strands of the first group and the strands of the secondgroup each intersect in the area of the length sections.
 8. The insertof claim 1, wherein the number of meanderings of each strand of thefirst group is twice as great as the number of meanderings of thecorresponding strand of the second group.
 9. The insert of claim 1,wherein the strands of the first group in the expanded state of theinsert are stretched essentially to form a circular ring.
 10. The insertof claim 1, wherein the strands in both groups of rings are containedentirely in the tubular circumferential surface.